The present invention relates to heat-curable silicone rubber compositions and, in particular, relates to heat-curable silicone rubber compositions which are self-bonding to various substrates, such as plastics, metals or glass.
Heat-curable silicone rubber is applied to various substrates for various purposes. It may, for instance, be applied to various synthetic fiber substrates, such as dacron or nylon, which imparts enhanced physical properties to the resulting laminate so that the laminate can be used for such purposes as gaskets, radiator hoses and the like. Further, for various reasons, it is desirable to apply heat-curable rubber to various hard substrates, such as metals or glass, so as to impart improved weatherability to the resulting laminated product.
At the present time, when heat-curable rubber is applied to various substrates, it is necessary to employ a primer, that is, a primer is applied on the surface of the substrate and then the silicone rubber composition is applied thereover and cured onto the substrate. If the silicone rubber composition is applied to the substrate without a primer, then in many cases the bond between the silicone rubber and the substrate is not as strong as would be desired. In discussing bonds, it is necessary to distinguish between two types of failure that may occur in the bonding between a silicone rubber layer and a substrate, that is cohesive failure and adhesive failure. Insofar as it relates to this application, adhesive failure occurs when the silicone rubber layer separates from the substrate at the point wherein the two layers meet, that is the bond between the silicone rubber layer and the substrate ruptures before the silicone rubber layer or the substrate. Cohesive failure occurs when the silicone rubber layer or the substrate rupture before the bond between the silicone rubber layer and the substrate fails.
In order to obtain cohesive failure with the present silicone rubber materials, it is necessary in many cases to use a primer before the application of the silicone rubber layer to the substrate. However, the use of a primer entails an additional step in the preparation of the laminate and thus is costly, as well as time consuming.
Further, there are presently only a limited number of primers that can be used with silicone rubber materials. Further, when some of these primers are used, they produce results of adhesive failure rather than cohesive failure when the laminate is tested. In addition, with these primers that are known, it is not always possible to obtain cohesive failure in the laminate when the silicone rubber is applied to certain substrates. In the copending docket of DeZuba, Berger and Selin, Docket 8SI-1189, there is disclosed one type of self-bonding, heat-curable silicone rubber composition. In the present case, there is disclosed another type of self-bonding, heat-curable silicone rubber composition.
Accordingly, it is one object of the present invention to provide a heat-curable silicone rubber composition that is self-bonding to all types of substrates.
It is another object of the present invention to provide a heat-curable silicone rubber composition that is self-bonding to various substrates and has good physical properties.
It is yet another object of the present invention to provide a heat-curable silicone rubber composition that will self-bond to various substrates and results in cohesive failure when tension is applied to separate the rubber composition from the substrate.
It is an additional object of the present invention to provide a process for producing a heat-curable silicone rubber composition that is self-bonding to all types of substrates and which can be used and applied immediately to any substrate without the use of a primer.
These and other objects of the present invention are accomplished by means of the composition and process set forth below.